mine's doing the same. there was someone a while back put
this stuff on and it looked pretty good but ofc fake carbon isnt to everyones taste. I dont know that anything will restore the colour once its faded, polytrol may darken it but ive found most of these treatments are only temporary measures, they 're-wet' the plastic but the oils evaporate pretty quickly. I thought about painting them but decided just to live with it as at least its consistent.
a word of warning; they're very brittle plastics at this age so be careful if youre removing/refitting them.